1. Field of the Invention
This invention relates to metal chain-belts especially adapted to connect the pulleys of a pulley transmission, particularly a continuously variable transmission (CVT), and broadly comprises a tension member or carrier constructed of a plurality of interlaced links arranged in transverse sets with the adjacent sets joined by pivot means, and load blocks carried by the carrier for engaging the pulleys.
2. Background Information
Variable pulley transmissions for transferring torque from an input or drive shaft to an output or driven shaft have been used for some time. In these transmissions, a first pulley constructed of a pair of flanges, at least one of which is conical, is mounted on the input shaft such that at least one of its flanges is axially movable with respect to its other flange. A second, similarly constructed and adjustable pulley is mounted on the output shaft. A flexible belt connects the two pulleys to transfer torque therebetween when the input shaft is driven. As the effective diameter of one pulley is changed, the effective diameter of the other pulley is changed in the other direction and, the drive ratio between the input and output shafts is adjusted in a smooth, continuous manner.
Automotive engineers have long recognized that the maximum operating efficiency of the engine could be achieved if the transmission could be controlled by adjusting to different loads and speed ratios, such that the engine is maintained and operated at its maximum efficiency operating conditions. This has not been possible when a conventional geared transmission is teamed with an engine. In the conventional geared transmission, the drive ratio is adjusted in discrete steps, rather than continuously. Accordingly, efforts have been directed to the use of a continuously variable transmission (CVT) of the type described above. The efforts have resulted in the production and marketing in Europe of the DAF passenger car, using flexible, continuous rubber belt to drivingly interconnect the pulleys. Rubber belts have been considered to be inferior to metal belts because of various adverse conditions under which they must operate. More recently, Fiat and Volvo have produced automobiles incorporating CVTs using respectively, metal belts and rubber belts. Some of the efforts to produce metal belts which are durable, relatively quiet in operation, and also economical to market, are described in the patent and other literature.
Flexible metal belts for use in CVTs are generally of two varieties, those referred to as "push" belts and those referred to as "pull" belts. Push belts are currently being used in the Fiat automobile's CVT. An example of a push belt is described in Van Doorne et al U.S. Pat. No. 3,720,113 and an example of a pull belt is described in Cole, Jr. et al U.S. Pat. No. 4,313,730. The Van Doorne et al belt comprises an endless carrier constructed of a plurality of nested metal bands and an endless array of generally trapezoidal (when viewed from the front) load blocks encircling the carrier and longitudinally movable therealong. Each block has edge surfaces engaging the pulley's flanges of a pulley transmission to transmit torque between the pulleys. The pull belt of Cole, Jr. et al utilizes an endless chain as the carrier, the sets of links of which are pivotably interconnected by pivot means. Load blocks, similar to those of Van Doorne et al, encircle the links; however the load blocks are constrained against longitudinal movement along the chain by the pivot means.
The push belt as described in relatively expensive to manufacture and must be installed and/or replaced as a complete, endless loop. Thus disassembly of parts of the pulley transmission is required, not only for the initial assembly, but also for replacement due to failure of one or more load blocks or one or more of the carrier bands.
The pull belt offers a less expensive alternative to the push belt. No precise matching of carrier parts is required. The belt can be assembled with a finite length, positioned around the pulleys, and the ends then connected by a pivot member. Thus disassembly of the pulleys is not required in either for initial installation or replacement of a belt.
Theoretically a load block, either on a push belt or pull belt, enters a pulley tangentially, so that the block is radially oriented with respect to the pulley. Actually, the block can tilt and probably enters the pulley at some other angle. When the load blocks tilt, at least one of the defining walls, usually the bottom wall, of the block's "window" or "windows", i.e., the opening or openings in which the carrier is located, digs into the carrier and damages the carrier. This damage can become so severe as to seriously weaken the carrier which leads to its premature failure. The idea of making the defining lower (and at times the upper) defining wall of the window or windows slightly round or arcuate from front-to-back has been suggested but has not been proven to be successful to aleviate the problem.